EP2023944A2 - Pre-b cell proliferation and lymphoblastic leukemia/high-grade lymphoma in mir155 transgenic mice - Google Patents

Abstract

A transgenic non-human animal, such as a mouse, has a genome that include a nucleic acid construct having at least one transcriptional regulatory sequence capable of directing expression in B cells of the animal, wherein the transcriptional regulatory sequence is operably linked to a nucleic acid encoding a miR155 gene product. A method of testing the therapeutic efficacy of an agent in treating or preventing a lymphoproliferative condition includes assessing the effect(s) of the agent on a transgenic non-human animal.

Description

PRE-B CELL PROLIFERATION AND LYMPHOBLASTIC LEUKEMIA/HIGH-GRADE LYMPHOMA IN miR155 TRANSGENIC MICE

Inventor: Carlo M. Croce

GOVERNMENT SUPPORT

[0001] The invention was supported, in whole or in part, by a grant from the U.S. Government. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

[0002] Acute leukemia is a rapidly progressive malignant disease of the bone marrow and blood that results in the accumulation of immature, fiinctionless cells, called blast cells, in the marrow and blood. The accumulation of blast cells in the marrow blocks normal blood cell development. As a result, red cells, white cells and platelets are not produced in sufficient numbers. When the disease originates in a marrow lymphocyte progenitor cell, it results in acute lymphoblastic leukemia (ALL) and when the disease originates in a myeloid progenitor, it results in acute myelogenous leukemia (AML).

[0003] ALL is a rapidly progressive cancer that starts by the malignant transformation of a marrow lymphocyte. ALL is the most common type of childhood leukemia, with 3,000 new cases per year in all age groups. The transformed, now malignant, cell multiplies and accumulates in the marrow as leukemic lymphoblasts. The lymphoblasts block normal blood cell-formation in the marrow, resulting in insufficient production of red cells, white cells and platelets.

[0004] High-grade lymphomas, also known as aggressive lymphoma, include several subtypes of lymphoma that progress relatively rapidly if untreated. These subtypes include, e.g., AIDS-associated lymphoma, anaplastic large cell lymphoma, Burkitt's lymphoma, diffuse large cell lymphoma, immunoblastic lymphoma, lymphoblastic lymphoma and small noncleaved cell lymphomas. Compared to diffuse large B~cell lymphomas, high-grade lymphomas behave more aggressively, require more intensive chemotherapy, and occur more often in children. Because rapidly dividing cells are more sensitive to anti-cancer agents and because the young patients usually lack other health problems, some of these lymphomas show a dramatic response to therapy. Acute lymphoblastic leukemia and high-grade lymphoma are the most common leukemias and lymphomas in children. These diseases are, for the most part, polyclonal, suggesting that only a few genetic changes are sufficient to induce malignancy.

[0005] MicroRNAs (miRNAs) represent a new class of abundant small RNAs that play important regulatory roles at the post-transcriptional level by binding to targeted mRNAs and either blocking their translation or initiating their degradation, according to the degree of complementarity with the target. Since their discovery in 1993 in Caenorhabditis elegans (Lee, R. et al., Cell 75:843-854 (1993)), there have been numerous reports that implicated these tiny molecules in the posttranscriptional regulation of a large array of proteins with very diverse roles, ranging from cell proliferation and differentiation to lipid metabolism (Nairz, K., et al., Dev. Biol. 291:314-324 (2006); Chen, J.F., etal, Nat. Genet. 33:228-233 (2006); Naguibneva, L, et al, Nat. Cell Biol. 8:278-284 (2006); Esau, C, etal, CellMetab. 3:87-98 (2006); and Gauthier, B.R., et al, Nat. Med. /2:36-18 (2006)).

[0006] mϊRNA profiling of hematopoietic lineages in humans and mice showed that miRNAs are differentially expressed in the course of hematopoietic development, suggesting a potential role in hematopoietic differentiation (Chen, C.Z., et al, Science 303:83-86 (2004); Chen, C.Z., et al., Semin. Immunol. 77:155-165 (2005); and Ramkissoon, S.H., et al, Leuk. Res. 30:643-647 (2006)). We have shown that miR-15^'a and miR-16-1 are deleted or down-regulated in 68% of cases of chronic lymphocytic leukemia (CLL) (Calin, G.A., et al, Proc. Natl Acad Sci. USA 99: 15524-15529 (2002); and Calin, G.A., et al, Proc. Natl Acad. ScL USA 101:U755-\ 1760 (2004)), and that miRNAs genes are frequently located at fragile sites and genomic regions involved in cancers (Calin, G.A., etal, Proc. Natl. Acad. Sci. USA 101:2999-3004 (2004)). miR155 and BIC (its host gene) transcripts have been shown to accumulate in human B cell lymphomas, especially diffuse large B cell lymphomas (Eis, P.S., et al, Proc. Natl Acad. ScL USA /02:3627-3632 (2005)), Hodgkin lymphomas (Kluvier, J., etal, J. Pathol 207:243-249 (2006)), and certain types of Burkitt lymphomas (latency type III Epstein- Barr virus-positive Burkitt lymphoma) (Kluvier, J., et al, Genes Chromosomes Cancer 45:147-153 (2006)).

[0007] Currently, there is an urgent need to produce animal models that can be used to screen for, and identify, candidate agents that have therapeutic potential for the treatment of lymphoproliferative disorders, such as B cell malignancies (e.g., B cell leukemias, B cell lymphomas). SUMMARY OF THE INVENTION

[0008] The present invention is based on the discovery that transgenic mice carrying a miRl 55 transgene, whose expression is targeted to B cells (e.g., using an Ig heavy chain- Eμ enhancer), initially exhibit a preleukemic pre-B cell proliferation, evident in spleen and bone marrow, and later develop B cell malignancies. Transgenic mice that overexpress miRl 55 develop a lymphoproliferative disease resembling human lymphoproliferative diseases, thus strongly implicating miRl 55 in the initiation and/or progression of these diseases. The Eμ-mmu-miR155 transgenic mice are useful for devising new therapeutic approaches to treat different forms of lymphoproliferative disorders, such as B cell malignancies (e.g., acute lymphoblastic leukemia, high-grade lymphomas) in humans. [0009] Accordingly, in one aspect, there is provided herein, novel animal models for lymphoproliferative disorders. Specifically, according to one aspect, animal models for B cell malignancies (e.g., Ieukemias (e.g., acute lymphoblastic leukemia), lymphomas (e.g., high-grade lymphoma), and neoplasms) are provided.

[00010] In one embodiment, there is provided herein a transgenic non-human animal (e.g., a mouse) whose genome comprises a nucleic acid construct comprising at least one transcriptional regulatory sequence capable of directing expression in B cells of the animal, operably linked to a nucleic acid encoding a miRl 55 gene product. In a particular embodiment, the miRl 55 gene product comprises a nucleotide sequence having at least 90% sequence identity to SEQ ID NO:1 and/or SEQ ID NO:2. In another embodiment, the miRl 55 gene product comprises the nucleotide sequence of SEQ ID NO:1. In still another embodiment, the miRl 55 gene product comprises the nucleotide sequence of SEQ ID NO:2.

[00011] According to one embodiment, the at least one transcriptional regulatory sequence can be any sequence capable of directing expression in B cells of the animal. In one embodiment, the transcriptional regulatory sequence comprises a V_H promoter (e.g., a V_H promoter derived from mouse). In another embodiment the transcriptional regulatory sequence comprises an Ig heavy chain-Eμ enhancer (e.g., an Ig heavy chain-Eμ enhancer derived from mouse). In a related embodiment, the nucleic acid construct comprises the 3' UTR and poly(A) sequence of a β-globin gene (e.g., a β-globin gene derived from human or other mammalian species). [00012] There is also provided herein a transgenic non-human animal whose genome comprises a nucleic acid construct comprising a V_H promoter and an Ig heavy chain-Eμ " enhancer, operably linked to a nucleic acid encoding a miR155 gene product comprising SEQ ID NO:1 and/or SEQ ID NO:2. In a particular embodiment, the transgenic non- human animal's genome comprises a nucleic acid construct comprising a V_H promoter and an Ig heavy chain-Eμ enhancer, operably linked to a nucleic acid encoding a miR155 gene product comprising a nucleotide sequence having at least 90% sequence identity to SEQ ID NO:1 and/or SEQ ID NO:2.

[00013] In a particular embodiment, the transgenic non-human animal has an expanded population of B2201ow/CD19^low/CD10^low/IgMYTCR7CD43- lymphoid cells in the spleen, the bone marrow or both the spleen and bone marrow, relative to this population in a suitable control animal. In a related embodiment, the transgenic non-human animal exhibits a lymphoproliferative condition. In a certain embodiment, the lymphoproliferative condition is a B cell malignancy (e.g., a B cell leukemia, for example, acute lymphoblastic leukemia; a B cell lymphoma, a B cell neoplasm). In a further embodiment, the B cell malignancy exhibits characteristics of human acute lymphoblastic leukemia, human lymphoblastic lymphoma or a combination thereof. In yet another embodiment, the lymphoproliferative condition is a preleukemic state (e.g., pre-B cell proliferation). In additional embodiments, the transgenic non-human animal exhibits an enlarged abdomen, splenomegaly, bone marrow replacement, lymphopenia, or a combination thereof.

[00014] There is also provided herein a method of testing the therapeutic efficacy of an agent in treating or preventing a lymphoproliferative condition in a subject. According to one embodiment, the method comprises administering the agent to a transgenic non-human animal (e.g., a mouse) whose genome comprises a nucleic acid construct comprising at least one transcriptional regulatory sequence capable of directing expression in B cells of the animal (e.g., a V_H promoter, an Ig heavy chain-Eμ enhancer, a combination thereof), wherein the transcriptional regulatory sequence is operably linked to a nucleic acid encoding a miR155 gene product comprising a nucleotide sequence having at least 90% sequence identity to SEQ ID NO: 1 and/or SEQ ID NO:2. In a particular embodiment, the miR155 gene product comprises the nucleotide sequence of SEQ ID NO:1. In another embodiment, the miR155 gene product comprises the nucleotide sequence of SEQ ID NO:2. [00015] After the agent has been administered to the transgenic animal, one or more symptoms and/or indications of the lymphoproliferative condition in the transgenic animal are compared with those of a control animal of the same genotype, which has not been administered the agent. If the agent inhibits, prevents and/or reduces one or more symptoms and/or indications of the lymphoproliferative condition in the transgenic animal to which it has been administered, relative to the control animal, then the agent is considered to have therapeutic efficacy in treating or preventing a lymphoproliferative condition. In a certain embodiment, the one or more symptoms and/or indications of the lymphoproliferative condition are selected from the group consisting of: an expanded population of B220^low/CD19^low/CD10^!ow/ IgM7TCR7CD43^" lymphoid cells, an enlarged abdomen, splenomegaly, bone marrow replacement, lymphopenia and a combination thereof.

[00016] In another embodiment, there is provided herein a method of determining whether an agent affects a lymphoproliferative condition in a subject (e.g., affecting a difference in the detectability and/or rate of appearance of one or more symptoms and/or indications of a lymphoproliferative condition). The method comprises administering an agent to a transgenic non-human animal described herein and comparing one or more symptoms and/or indications of the lymphoproliferative condition in the transgenic animal to those of a control animal of the same genotype, wherein the control animal has not been administered the agent. Detection of a difference in the detectability and/or rate of appearance of one or more symptoms and/or indications of the lymphoproliferative condition in the transgenic animal, relative to the control animal, is indicative of the agent affecting the lymphoproliferative condition.

[00017] In one embodiment, the lymphoproliferative condition is a B cell malignancy. In a particular embodiment, the B cell malignancy is selected from the group consisting of acute lymphoblastic leukemia, B cell lymphoma (e.g., high-grade lymphoma), B cell neoplasm and a combination thereof. The B cell malignancy may exhibit characteristics of human acute lymphoblastic leukemia, human lymphoblastic lymphoma or both. In another embodiment, the lymphoproliferative condition is a preleukemic state, such as a state characterized by pre-B cell proliferation.

[00018] These as well as other important aspects of the invention will become more apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS [00019] The patent or application file contains at least one drawing executed in color.

Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee. [00020] FIG. 1 is schematic diagram depicting the miR155 transgene construct that was injected in the male pronuclei of the oocytes of pregnant C57/B6 and FVB/N female mice.

The miR155 transgene construct was made by inserting the mmu-miR155 gene between the EcoRV and Sail sites, downstream from the V_H promoter Eμ enhancer. [00021] FIG. 2A is a Southern blot depicting the genotype of the seven miR155 transgenic founders (lanes 1, 3, 5, 6, 7, 10 and 14) and eight wild-type (lanes 2, 4, 8, 9, 11,

12, 13 and 15) mice with a C57BL/6 background. [00022] FIG. 2B is a Southern blot depicting the genotype of eight miR155 transgenic founders (lanes 1, 3, 5, 7, 9, 11, 13 and 15) and seven wild-type (lanes 2, 4, 6, 8, 10, 12 and

14) mice with an FVB/Nf background. [00023] FIG. 3 is a Northern blot on total RNA depicting expression of mature miRl 55 in lymphocytes that were isolated from the spleens of 3-week-old mice from 6 of the 15 transgenic lines, using the antisense oligonucleotide of the mmu-miR155 mature sequence as a probe. The five transgenic lines with the highest level of expression of mature miRl 55 in the splenocytes (lanes 1, 2, 5, 8 and 9) were selected for further breeding and analysis.

One transgenic line did not express the transgene (lane 3). Trangene expression was absent from the wild-type controls (lanes 4, 6 and T). [00024] FIG. 4A is a photograph showing a transgenic mouse with a considerably enlarged abdomen (left), due to clinically-evident splenomegaly, relative to a wild-type mouse, at an age of 6 months. [00025] FIG. 4B is a photograph depicting the spleens of the mice shown in FIG. 4A.

The spleen of the transgenic mouse (left) is enlarged due to expansion of leukemic/lymphoma cells. [00026] FIG. 5A is a micrograph depicting a hematoxylin/eosin (H&E)-stained section of spleen from a 3 week old transgenic mouse (mouse no. 50; founder no. 10) at 200 X magnification. The section displays atypical lymphoid proliferation compressing the white pulp. [00027] FIG. 5B is a micrograph depicting an H&E-stained section of spleen from a 6 month old trangenic mouse (founder no. 8) at 100 X magnification. The overall architecture of the spleen is being replaced by atypical lymphoid proliferation. Only a few germinal lymphoid follicles remain, which are greatly decreased in size and compressed by the proliferation.

[00028] FlG. 5C is a micrograph depicting an H&E-stained section of spleen from a 6 month old trangenic mouse (founder no. 8) at 200 X magnification. The spleen architecture has been almost completely effaced by the lymphoblastic proliferation. ^• Remnants of 2 small compressed lymphoid follicles are visible.

[00029] FIG. 5D is a micrograph depicting an H&E-stained section of bone marrow from a 6 month old trangenic mouse (founder no. 8) at 400 X magnification, showing the lymphoblastic proliferation in the bone marrow that leads to the replacement of the hemtopoietic foci.

[00030] FIG. 5E is a micrograph depicting an H&E-stained section of normal spleen at 200 X magnification.

[00031] FIG. 5F is a micrograph depicting a section of spleen from a 3 week old transgenic mouse (mouse no. 72) at 200 X magnification. The section has been stained for Ki67 and shows increased lymphoid proliferation in the spleen.

[00032] FIG. 6 is a micrograph at 400 X magnification depicting atypical lymphoid proliferation in a section of spleen from a 3 week old transgenic mouse (mouse no. 50), which has been immunohistochemically-stained for IgM. IgM is present in the cytoplasm of the proliferating lymphocytes (clgM) as a brown perinuclear halo in the transgenic mice, whereas the wild-type lymphocytes are intensely brown, with no distinct nuclei, due to the presence of both slgM and clgM.

[00033] FIG. 7A is a flow cytometry analysis profile depicting an expansion of a B220^low/CD19^low/CD10^low/ϊgM7TCR7CD43^" population of lymphocytes in the spleen of transgenic mice from two different lines of founders (founders 8 and 10). Gated splenocytes for two transgenic mice and two wild type mice at 3 weeks of age (transgenic mouse no. 74, founder 8 (74TG; upper left) and wild-type mouse no. 68 (68WT; upper right)) and 7 weeks of age (transgenic mouse no. 156, founder 10 (156TG; bottom left) and wild-type mouse no. 157 (157WT; bottom right)) are shown. Comparison of the upper left quadrants of the plots, gating the B220⁺ IgM population, shows an increase in the number of precursor B cells in the trangenic spleen, relative to wild type.

[00034] FIG. 7B is a flow cytometry analysis profile depicting an expansion of a B220^low/CD19^low/CD10^low/IgM7TCRVCD43^" population of lymphocytes in the bone marrow of a transgenic mouse from founder 8. Gated bone marrow white blood cells for one transgenic and one wild-type mouse at 6 months of age (transgenic mouse no. 8, (8TG; left) and wild-type mouse no. 24 (24WT; right)) are shown. Comparison of the upper right quadrants of the two plots indicates a decrease in the B200⁺ IgM⁺ gated mature B cell population of the bone marrow of the transgenic mouse, relative to the wild-type mouse.

[00035] FIG. 8 A is a graph depicting B220-PE expression as evaluated by flow cytometry analysis on B220⁺-gated splenocytes of wild-type mouse no.223 (223 WT) at 7 weeks of age.

[00036] FIG. 8B is a graph depicting CDlO-FITC expression as evaluated by flow cytometry analysis on B220⁺-gated splenocytes of wild-type mouse no. 223 (223 WT) at 7 weeks of age.

[00037] FIG. 8C is a graph depicting B220-PE expression as evaluated by flow cytometry analysis on B220⁺-gated splenocytes of transgenic mouse no. 222 (222TG) at 7 weeks of age, showing a noticeable increase in the B220^low population (intercalated between the two peaks of B220^" and B220⁺) in the transgenic mouse, relative to the wild-type mouse.

[00038] FIG. 8D is a graph depicting CDl 0-FITC expression as evaluated by flow cytometry analysis on B220⁺-gated splenocytes of transgenic mouse no. 222 (222TG) at 7 weeks of age, showing an increase in the percentage of the CDlO⁺ population in the

[00039] B220⁺-gated population only in the transgenic mouse relative to the wild-type mouse, demonstrating that the B220^low proliferation is due, at least in part, to an increase of the CDlO⁺ population.

[00040] FIG. 8E is a graph depicting B220-PE expression as evaluated by flow cytometry analysis on B220⁺-gated splenocytes of transgenic mouse no. 221 (221TG) at 7 weeks of age, showing a noticeable increase in the B220^low population (intercalated between the two peaks of B220^* and B220⁺) in the transgenic mouse, relative to the wild-type mouse.

[00041] FIG. 8F is a graph depicting CDlO-FITC expression as evaluated by flow cytometry analysis on B220⁺-gated splenocytes of transgenic mouse no. 221 (221TG) at 7 weeks of age, showing an increase in the percentage of the CDIO⁺ population in the

[00042] B220⁺-gated population only in the transgenic mouse relative to the wild-type mouse, demonstrating that the B220^low proliferation is due, at least in part, to an increase of the CDlO⁺ population.

[00043] FIG. 9 is a karyotype of lymphoid cells isolated from a transgenic spleen, analyzed for chromosomal deletions, translocations and inversions, as well as the number of metaphases. The arrow indicates an abnormality in Chromosome 9, which was identified by the presence of a thick extra band.

[00044] FIG. 10 is a Southern blot on DNA extracted from the splenocytes of 5 transgenic (TG) and 4 wild-type (WT) mice between 3 and 6 weeks of age. Southern blot hybridization was performed using the JH4 probe and different digesting enzymes, as indicated at the top of the lanes (Stul, BgIII, BamHI, and Hindlll). The thick bands of high molecular weight correspond to the germ line. There are no rearranged bands in the transgenic animals, relative to wild type.

DETAILED DESCRIPTION OF THE INVENTION

[00045] A description of particular embodiments of the invention follows. [00046] As exemplified and described herein, transgenic mice that overexpress the microRNA, miR155, develop a lymphoproliferative disease resembling acute lymphoblastic leukemia and high-grade lymphoma in humans. The results provided herein strongly indicate that oncogenic expression of miRl 55 and/or other gene(s) (e.g., genes that are activated in cancer (e.g., signal transduction genes)) are involved in the initiation and/or progression of B cell malignancies. Accordingly, there is provided herein an animal model that may be used to investigate the mechanisms underlying the initiation and progression of B cell malignancies and other lymphoproliferative conditions. This animal model may also be used in the identification, development and testing of novel therapeutic agents that are useful in treating or preventing lymphoproliferative disorders.

[00047] In one embodiment, there is provided herein a transgenic animal whose genome comprises a nucleic acid construct or transgene comprising at least one transcriptional regulatory sequence capable of directing expression to B cells, wherein the transcriptional regulatory sequence is operably linked to a nucleic acid sequence encoding a miRl 55 gene product. The term "transgene" refers to a nucleic acid sequence introduced into one or more cells of a non-human animal by way of human intervention, such as by way of the methods described herein. The introduced genetic information may be foreign to the species of animal to which the recipient belongs, foreign only to the particular individual recipient, or genetic information already possessed by the recipient. In the latter case, the introduced genetic information may be differentially-expressed, as compared to the native endogenous gene. [00048] The transgenic non-human animals have a genome that comprises a nucleic acid construct/transgene, that is capable of expressing a miR155 gene product. As miR gene products, (also referred to herein as microRNAs, miRs and miRNAs) are not translated into protein, the term "miR gene product" does not include proteins. The unprocessed miR gene transcript is also called a "miR precursor," and typically comprises an RNA transcript of about 70-100 nucleotides in length. The miR precursor can be processed (e.g., through natural processing routes (e.g., using intact cells or cell lysates) or by synthetic processing routes (e.g., using isolated processing enzymes, such as isolated Dicer, Argonaut, or RNAse III (e.g., E. coli RNAse III)) into an active 19-25 nucleotide RNA molecule. This active 19-25 nucleotide RNA molecule is also called the "processed" miR gene transcript or "mature" miRNA. When a microRNA is referred to herein by name, the name corresponds to both the precursor and mature forms, unless otherwise indicated.

[00049] As used herein, "miR155 gene product" refers to the unprocessed (e.g., precursor) or processed (e.g., mature) RNA transcript from a miR155 gene, such as, but not limited to, a miR155 gene from mouse (Mus musculus). The precursor miR155 gene product from mouse is represented by the nucleotide sequence: 5'-

CUGUUAAUGCUAAUUGUGAUAGGGGUUUUGGCCUCUGACUGACUCCUACCU GUU AGCAUU AAC AG-3' (SEQ IDNO:1), while the processed, or mature, mouse miR] 55 gene product is represented by the nucleotide sequence: 5'- UUAAUGCUAAUUGUGAUAGGGG-3' (SEQ ID NO:2; GenBank Accession No. AJ459767).

[00050] In certain embodiments, the miR155 gene product comprises a nucleotide sequence having at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 99%, or 100%, sequence identity to the nucleotide sequences of SEQ ID NO:1 and/or SEQ ID NO:2. In a particular embodiment, the miR155 gene product comprises a nucleotide sequence having 100% identity to the nucleotide sequence of SEQ ID NO:1. In another embodiment, the miR155 gene product comprises a nucleotide sequence having 100% identity to the nucleotide sequence of SEQ ID NO:2.

[00051] The actual comparison of two sequences can be accomplished by well-known methods, for example, using a mathematical algorithm. A preferred, non-limiting example of such a mathematical algorithm is described in Karlin et al. (Proc. Natl. Acad. ScL USA, 90:5873-5877 (1993)). Such an algorithm is incorporated into the BLASTN and BLASTX programs (version 2.2) as described in Schaffer et al. (Nucleic Acids Res., 2P:2994-3005 (2001)). When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g., BLASTN; available at the Internet site for the National Center for Biotechnology Information) can be used. In one embodiment, the database searched is a non-redundant (NR) database, and parameters for sequence comparison can be set at: no filters; Expect value of 10; Word Size of 3; the Matrix is BLOSUM62; and Gap Costs have an Existence of 11 and an Extension of 1.

[00052] Another non-limiting example of a mathematical algorithm utilized for the comparison of sequences is the algorithm of Myers and Miller, CABIOS (1989). Such an algorithm is incorporated into the ALIGN program (version 2.0), which is part of the GCG (Accelrys, San Diego, California) sequence alignment software package. When utilizing the ALIGN program for comparing amino acid sequences, a PAM120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used. Additional algorithms for sequence analysis are known in the art and include ADVANCE and ADAM as described in Torellis and Robotti (Comput. Appl. Biosci., 10: 3-5, 1994); and FASTA described in Pearson and Lipman (Proc. Natl. Acad. Sci USA, 85: 2444-2448, 1988).

[00053] In another embodiment, the percent identity between two amino acid sequenees can be accomplished using the GAP program in the GCG software package (Accelrys, San Diego, California) using either a Blossom 63 matrix or a PAM250 matrix, and a gap weight of 12, 10, 8, 6, or 4, and a length weight of 2, 3, or 4. In yet another embodiment, the percent identity between two nucleic acid sequences can be accomplished using the GAP program in the GCG software package (Accelrys, San Diego, California), using a gap weight of 50 and a length weight of 3.

[00054] According to one aspect, the transgenic non-human animal possesses a genome that comprises a nucleic acid construct in which a nucleic acid sequence encoding a miR155 gene product is operably linked to at least one transcriptional regulatory sequence capable of directing expression in B cells of the animal. The term "transcriptional regulatory sequence" is used according to its art-recognized meaning. It is intended to mean any DNA sequence that can, by virtue of its sequence, cause the linked gene to be either up- or down-regulated in a particular cell. In the case of a promoter, the promoter will generally be adjacent to the coding region. In the case of an enhancer, however, the enhancer may function at some distance from the coding region, such that there is an intervening DNA sequence between the enhancer and the coding region. To direct expression of the genetic information, which may include a DNA sequence encoding a particular protein (or "coding region"), the coding region of interest may be coupled to at least one transcriptional regulatory sequence in a functional manner. Transcriptional regulatory sequences may be used to increase, decrease, regulate or designate to certain tissues or to certain stages of development, the expression of a gene. The transcriptional regulatory sequences need not be naturally occurring sequences.

[00055] Thus, in one embodiment described herein, a sequence encoding miR155 is operably linked to transcriptional regulatory sequence(s) directing expression to B cells, to generate a recombinant construct or transgene. The transcriptional regulatory sequence can be any sequence capable of directing expression in B cells. Examples of suitable transcriptional regulatory sequence include, but are not limited to, a V_H promoter, an Ig heavy chain-Eμ enhancer and a combination thereof. In a particular embodiment, the transcriptional regulatory sequence is a mouse transcriptional regulatory sequence or a transcriptional regulatory sequence derived from mouse.

[00056] A nucleic acid molecule is said to be "capable of expressing" or "capable of directing expression of a microRNA if it contains nucleotide sequence(s) that contain transcriptional regulatory information, and such sequence(s) are "operably linked" to nucleotide sequence(s) that encode the microRNA. An operable linkage is a linkage in which regulatory nucleic acid sequence(s) and the nucleic acid sequence(s) sought to be expressed are connected in such a way as to permit gene expression.

[00057] In general, the regulatory regions needed for gene expression include, but are not limited to, transcriptional regulatory sequences (e.g., a promoter region, an enhancer region), as well as DNA sequence(s) that, when transcribed into RNA, contribute to the stability of the gene transcript.

[00058] The term "promoter" is used according to its art-recognized meaning. It is intended to mean the DNA region, usually upstream to the coding sequence of a gene or operon, which binds RNA polymerase and directs the enzyme to the correct transcriptional start site. A promoter region is operably linked to a DNA sequence if the promoter is capable of effecting transcription of that DNA sequence.

[00059] The term "enhancer" is used according to its art-recognized meaning. It is intended to mean a sequence found in eukaryotes and certain eukaryotic viruses, which can increase transcription from a gene when located (in either orientation) up to several kilobases from the gene being studied. These sequences usually act as enhancers when on the 5' side (upstream) of the gene in question. However, some enhancers are active when placed on the 3' side (downstream) of the gene. In some cases, enhancer elements can activate transcription from a gene with no (known) promoter.

[00060]." The nucleic acid construct may also include sequences that promote expression and/or stability of the construct and/or a gene product expressed from the construct. In a particular embodiment, the nucleic acid construct comprises the 3' UTR and poly(A) sequence of a β-globin gene (e.g., a mouse β-globin gene). Other sequences that promote expression and/or stability of the construct and/or a gene product expressed from the construct are known in the art and are encompassed herein.

[00061] The term "transgenic non-human animal" is used herein to include all vertebrate animals, except humans. In one embodiment, the transgenic non-human animal is a mammal. Such transgenic non-human animals include, for example, transgenic pigs, transgenic rats, transgenic rabbits, transgenic cattle, transgenic goats, and other transgenic animal species, particularly mammalian species. Additionally, other members of the rodent family, e.g., rats, and guinea pigs, and nonhuman primates, such as chimpanzees, may be used to practice the embodiments described herein. In a particular embodiment, the transgenic non-human animal is a mouse. The transgenic non-human animals described herein include individual animals in all stages of development, including embryonic and fetal stages.

[00062] A "transgenic animal" is an animal containing one or more cells bearing genetic information received, directly or indirectly, by deliberate genetic manipulation at a subcellular level, such as by microinjection or infection with a recombinant virus. The introduced nucleic acid molecule may be integrated within a chromosome, or it may be extra-chromosomally replicating DNA. Suitable transgenic animals described herein include, but are not limited to, those animals in which the genetic information was introduced into a germ line cell, thereby conferring the ability to transfer the information to offspring. If such offspring in fact possess some or all of that information, then they, too, are transgenic animals.

[00063] To produce transgenic animals, any method known in the art for introducing a recombinant construct or transgene into an embryo, such as, for example, microinjection, use of a cell gun, transfection, liposome fusion, electroporation, and the like, may be used. In a particular embodiment, the method for producing a transgenic animal is microinjection, which involves injecting a DNA molecule into the male pronucleus of a fertilized egg (see, e.g., U.S. Pat. Nos. 4,870,009; 5,550,316; 4,736,866; and 4,873,191). Methods for introducing a recombinant construct/transgene into mammals and their germ cells were originally developed in the mouse. Such methods were subsequently adopted for use with larger animals, including livestock species (see, e.g., PCT Publications Nos. WO 88/00239, WO 90/05188 and WO 92/11757). Microinjection of DNA into the cytoplasm of a zygote can also be used to produce transgenic animals.

[00064] The methods for evaluating the presence of the introduced transgene as well as its expression are readily available and well-known in the art. Such methods include, but are not limited to, DNA (Southern) hybridization to detect the exogenous DNA, polymerase chain reaction (PCR), polyacrylamide gel electrophoresis (PAGE) and blots to detect DNA, RNA or protein.

[00065] The present embodiments are not limited to any one species of animal, but provides for any appropriate non-human vertebrate species. For example, as described and exemplified herein, transgenic mice can be produced. Other non-limiting examples include, e.g., other non-human mammals described herein, such as guinea pigs, rabbits, pigs, sheep, etc. The success rate for producing transgenic animals by microinjection is highest in mice, where approximately 25% of fertilized mouse eggs into which the DNA has been injected, and which have been implanted in a female, will develop into transgenic mice. Lower success rates have been achieved with rabbits, pigs, sheep and cattle.

[00066] In a particular embodiment, the transgenic non-human animals described herein exhibit an expanded population of B220^low/CD19^low/CD10^Iow/ TgM7TCR7CD43^" lymphoid cells in the spleen, the bone marrow or both the spleen and bone marrow, relative to this population in a suitable control animal. As used herein, the term "expanded population of B220^|OW/CD19^|OW/CD10^|OW/ IgM7TCR7CD43- cells" or "increase of

B220^low/CD19^low/CD10^low/IgM^"/TCR7CD43^' cells" refers to a population of lymphoid cells that represents an increase in the number of B220^low/CD19^low/CDlθ'T/TgM7TCR7CD43- cells and/or the proportion of B220^low/CD19^low/CD10^low/IgM7TCR7CD43^" cells relative to other subtypes of lymphoid cells, as compared to that of a control animal.

[00067] In another embodiment, the transgenic non-human animals described herein exhibit a lymphoprolϊferative condition. "Lymphoproliferative" refers to that which pertains to, or is characterized by, proliferation of the cells of the lymphoreticular system; the term is generally used to refer to a group of malignant neoplasms. "Lymphoreticular" refers to the cells or tissues of both the lymphoid and reticuloendothelial systems. "Lymphoproliferative condition" (or "lymphoproliferative disease" or "lymphoproliferative disorder") refers to one of a group of malignant neoplasms arising from cells related to the common multipotential, primitive lymphoreticular cell that includes, among others, the lymphocytic, histiocytic, and monocytic leukemias, multiple myeloma, plasmacytoma, Hodgkin's disease, all lymphocytic lymphomas, and immunosecretory disorders associated with monoclonal gammopathy. As used herein, "lymphoproliferative disorder", "lymphoproliferative disease" or "lymphoproliferative condition" may also refer to a physiological state in which the proliferation, multiplication and/or accumulation of cells of the lymphoreticular system is altered relative to a normal or control animal, but the affected animal does not yet necessarily exhibit symptoms of one of the neoplasms described above. As used herein, a "preleukemic" state refers to such a lymphoproliferative condition that precedes the development of overt symptoms of leukemia.

[00068] In a certain embodiment, the lymphoproliferative condition is a B cell malignancy (e.g., a B cell leukemia (for example, acute lymphoblastic leukemia); a B cell lymphoma (e.g., high-grade lymphoma), a B cell neoplasm). In a further embodiment, the B cell malignancy exhibits characteristics of human acute lymphoblastic leukemia, human lymphoblastic lymphoma or a combination thereof. In yet another embodiment, the lymphoproliferative condition is a preleukemic state (e.g., pre-B cell proliferation). In additional embodiments, the transgenic non-human animal exhibits an enlarged abdomen, splenomegaly, bone marrow replacement, lymphopenia, or a combination thereof.

[00069] In another embodiment, there is described herein a method for the use of transgenic non-human animals as experimental models for the study of lymphoproliferative disorders (e.g., B cell malignancies (e.g., leukemias (e.g., acute lymphoblastic leukemia), lymphomas (e.g., high-grade lymphoma), and neoplasms)), and for testing potential carcinogenic and therapeutic agents.

[00070] In another aspect, there is described herein a method of testing the therapeutic efficacy of an agent in treating or preventing a lymphoproliferative condition in a subject. According to one embodiment, the method comprises administering the agent to a transgenic non-human animal (e.g., a mouse) described herein. In one embodiment, the transgenic non-human animal has a genome comprising a nucleic acid construct that comprises at least one transcriptional regulatory sequence capable of directing expression in B cells of the animal (e.g., a V_H promoter, an Ig heavy chain-Eμ enhancer, a combination thereof), wherein the transcriptional regulatory sequence is operably linked to a nucleic acid encoding a miR.155 gene product. In a particular embodiment, the transcriptional regulatory sequence is operably linked to a nucleotide sequence having at least 90% sequence identity to SEQ ID NO: 1 and/or SEQ ID NO:2. Tn another embodiment, the miR155 gene product comprises the nucleotide sequence of SEQ ID NO: 1. In yet another embodiment, the miRl 55 gene product comprises the nucleotide sequence of SEQ ID NO:2.

[00071] After the agent has been administered to the transgenic animal, one or more symptoms and/or indications of the lymphoproliferative condition in the transgenic animal are compared with those of a control animal of the same genotype, which has not been administered the agent. If the agent inhibits, prevents and/or reduces one or more symptoms and/or indications of the lymphoproliferative condition in the transgenic animal to which it has been administered, relative to the control animal, then the agent is considered to have therapeutic efficacy in treating or preventing a lymphoproliferative condition. In a certain embodiment, the one or more symptoms and/or indications of the lymphoproliferative condition are selected from the group consisting of: an expanded population of B220^low/CD19^low/CD10^low/ IgM^"/TCR7CD43^" lymphoid cells, enlarged abdomen, splenomegaly, bone marrow replacement, lymphopenia and a combination thereof.

[00072] Lymphoproliferative conditions that are suitable for testing the therapeutic efficacy of an agent include, for example, those described herein. In one embodiment, the lymphoproliferative condition is a B cell malignancy. In a particular embodiment, the B cell malignancy is selected from the group consisting of acute lymphoblastic leukemia, B cell lymphoma (e.g., high-grade lymphoma), B cell neoplasm and a combination thereof. The B cell malignancy may exhibit characteristics of human acute lymphoblastic leukemia, human lymphoblastic lymphoma or both. In another embodiment, the lymphoproliferative condition is a preleukemic state, such as a state characterized by pre-B cell proliferation.

[00073] As described herein, there is provided herein transgenic non-human animals that express miRl 55 in B cells. In one embodiment, a transgenic animal is provided whose genome comprises a nucleic acid construct or transgene comprising at least one transcriptional regulatory sequence capable of directing expression to B cells, wherein the transcriptional regulatory sequence is operably linked to a nucleic acid sequence encoding miRl 55. In a particular embodiment, the transgene comprises a DNA sequence encoding miRl 55 which has been placed under the transcriptional control of a VH promoter and/or an Ig heavy chain-Eμ enhancer. In such animals, mirl55 expression is directed to immature and mature B cells. In one embodiment, the transgenic animals are mice which develop an expanded population of B220^low/CD19^low/CD10^low/IgM^'/TCR7CD43^" lymphoid cells.

[00074] In another embodiment, white blood cells from a transgenic animal exhibiting lymphoproliferation may be transferred to a second animal (which may be a non-transgenic animal), thereby inducing a rapid onset of lymphoproliferative disease in the second "recipient" animal.

[00075] According to another embodiment, potential therapeutic modalities or agents for preventing and/or treating lymphoproliferative disorders may be tested by measuring the anti-lymphoproliferative activity of such modalities in animals produced according to one or more aspects as described herein. Such activity may be assessed by measuring the capacity of a potential therapeutic modality to inhibit, prevent, and/or destroy one or more of the symptoms or indications of lymphoproliferative disease exhibited by transgenic animals produced according to one embodiment and/or in "recipient" animals produced according to another embodiment.

[00076] A variety of therapeutic modalities or agents, such as proteins (e.g., antibodies), peptides, peptidomimetics, small organic molecules, nucleic acids and the like, can be tested for preventing and/or treating lymphoproliferative disorders. According to the methods described herein, agents can be individually screened or one or more agents can be tested simultaneously. Where a mixture of compounds is tested, the compounds selected by the processes described can be separated (as appropriate) and identified using suitable methods (e.g., sequencing, chromatography). The presence of one or more compounds in a test sample can also be determined according to these methods.

[00077] Agents that prevent and/or treat lymphoproliferative disorders can be identified, for example, by screening libraries or collections of molecules, such as, the Chemical Repository of the National Cancer Institute, in assays that measure inhibition and/or prevention of one or more of the symptoms or indications of lymphoproliferative disease exhibited by the transgenic animals described herein. Libraries, such as combinatorial libraries, of compounds (e.g., organic compounds, recombinant or synthetic peptides, "peptoids", nucleic acids) produced by combinatorial chemical synthesis or other methods can be tested (see e.g., Zuckerman, R.N. et al, J. Med. Chem., 37: 2678-2685 (1994) and references cited therein; see also, Ohlmeyer, M.H.J. et al., Proc. Natl. Acad. Sci. USA 90:10922-10926 (1993) and De Witt, S.H. etaL, Proc. Natl. Acad. Sci. USA 90:6909-6913 (1993), relating to tagged compounds; Rutter, WJ. et al. U.S. Patent No. 5,010,175; Huebner, V.D. et ah, U.S. Patent No. 5,182,366; and Geysen, H.M., U.S. Patent No. 4,833,092). Where compounds selected from a library carry unique tags, identification of individual compounds by chromatographic methods is possible.

[00078] Identified therapeutic modalities can further be formulated in accordance with known methods to produce pharmaceuticaJly-acceptable compositions. Therapeutic modalities or compositions comprising such therapeutic modalities may be administered to subjects (e.g., transgenic animals) in a variety of standard ways. For example, the agent can be administered using a variety of routes, including, for example, oral, dietary, topical, transdermal, rectal, parenteral (e.g., intravenous, intraarterial, intramuscular, subcutaneous, intradermal injection), and inhalation (e.g., intrabronchial, intranasal, oral inhalation, intranasal drops). Administration can be local or systemic as indicated. The preferred mode of administration can vary depending upon the antibody or antigen-binding fragment to be administered and the particular condition (e.g., disease) being treated, however, oral or parenteral administration is generally preferred.

[00079] Agents can be administered parenterally such as, for example, by intravenous, intramuscular, intrathecal or subcutaneous injection. Parenteral administration can be accomplished by incorporating the agent(s) into a solution or suspension. Such solutions or suspensions may also include sterile diluents, such as water for injection, saline solution, bacteriostatic saline (saline containing about 0.9% mg/ml benzyl alcohol), phosphate- buffered saline (referred to herein as PBS), Hank's solution, Ringer's-lactate, fixed oils, polyethylene glycols, glycerine, propylene glycol, and other synthetic solvents. Parenteral formulations may also include antibacterial agents (e.g., benzyl alcohol, methyl parabens), antioxidants (e.g., ascorbic acid, sodium bisulfite), and chelating agents (e.g., EDTA). Buffers, such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride and dextrose, may also be added. The parenteral preparation can be enclosed in ampules, disposable syringes, or multiple dose vials made of glass or plastic.

[00080] EXEMPLIFICATION

[00081] Example 1: Production of Eμ-mmu-miRl 55 transgenic mice.

[00082] Materials and Methods

[00083] Transgenic mice:

[00084] A 318-bp fragment containing the precursor sequence of miRl 55 was amplified by PCR from the genome of the 129SvJ mouse (The Jackson Laboratory) and cloned into the EcoRV and Sail sites of the pBSVE6BK (pEμ) plasmid, which contains the Eμ enhancer VH promoter for Ig heavy chains and the 3' UTR and the po!y(A) of the human β- globin gene (FIG. 1), and had been used previously for the development of chronic lymphocytic leukemia in Eμ-TCLl transgenic mice (Bichi, R., et al, Proc. Natl. Acad. Sci. USA 99:6955-6960 (2002)). The transgene, which was isolated by cutting the construct with BssHII and Pvul, was injected into the male pronucleus of fertilized oocytes of pregnant FVB/N and C57/B6 mice. Pups were screened for the presence of the transgene by Southern blot analysis, which was performed on tail-extracted DNA that was digested with BamHI, using a probe designed to target the Eμ enhancer sequence (FIGS. 2A, 2B). Transgenic founders were identified and bred to age-matched wild-type mice. Transgenic hemizygous mice were born, studied, and compared with their wild-type counterparts. Mice were genotyped by PCR performed on tail-extracted DNA (data not shown).

[00085] Northern Blot analysis:

[00086] Spleens were dissociated between two frosted slides, and the lysate was washed in phosphate buffered saline (PBS), depleted of red blood cells by hypotonic lysis with ammonium chloride (NH₄Cl), centrifuged, and resuspended in PBS. Total RNA was extracted with TRIzol Reagent (GIBCO, Invitrogen), loaded and denatured on SDS/PAGE, and blotted on a Hybond N⁺ membrane (Amersham Pharmacia). The membrane was hybridized with a γ-³²P radioactive probe containing the antisense of the mature mmu- miR155 sequence, incubated overnight, washed, and exposed to a Phosphor Imager screen (Molecular Dynamics). The image was processed using a Typhoon image processing system (Amersham Biosciences) (FIG. 3).

[00087] Results

[00088] Transgenic mice were generated in which mmu-miRl 55 (mouse miRl 55) expression is under the control of a V_H promoter-Ig heavy chain Eμ enhancer, which becomes active at the late pro-B cell stage of B cell development. Fifteen transgenic founders were identified by Southern blot hybridization (FIGS. 2A, 2B), seven on a C57BL/B6 background (designated F1-F7) and eight on an FVB/N background (designated F8-F15). These founders were bred to wild-type mice of the same strain to produce 15 independent transgenic lines.

[00089] Real-time PCR (data not shown) and Northern blot analysis (FIG. 3), performed on total RNA that was extracted from transgenic and wild-type spleens, showed high levels of miRl 55 expression for five founder lines of transgenic mice. One transgenic line lacked expression completely, while all other founder lines expressed the transgene. Wild-type mice did not express mature miR155 in the splenocytes, as previously reported (Monticelli, S., etal, Genome Biol. 6:R71 (2005)).

[00090] Example 2: Phenotypic characterization of Eμ-mmu-miR 155 transgenic mice reveals a pre-B cell proliferation in spleens and bone marrow, leading to B cell malignancies.

[00091 ] Materials and Methods

[00092] Somatic measurements:

[00093] Mice were weighed after being killed, and their spleens were dissected, measured and weighed.

[00094] White blood cell (WBC) and smear preparation:

[00095] Blood was drawn from retroorbital blood vessels of mice and either smeared on frosted slides and stained with Giemsa or centrifuged, washed in PBS, and treated with ammonium chloride. Cells were counted with a cell-counter chamber.

[00096] Flow Cytometry Analysis:

[00097] Single-cell suspensions of splenocytes or bone marrow cells were depleted of mature red blood cells by hypotonic lysis (0.165 MNH₄Cl) and stained with the following conjugated antibodies: anti-B220-PE, anti-IgM-FITC, anti-TCR-PE cy5, anti-CD5-PE, and anti-CD-43-FITC. All antibodies were obtained from BD PharMingen. Flow cytometry was carried out on a Becton Dickinson FACSCalibur, and data were analyzed using the Becton Dickinson FACS CONVERT 1.0 for Mac software.

[00098] Histology and Immunohistochemistry:

[00099] Spleens, femurs, and sternums were isolated from necropsied mice and fixed in 10% buffered formalin, included in paraffin, and then cut into 4 micron sections. The sections were stained with hematoxylin/eosin according to standard protocols. For the dewaxing step, sections were heated for 1 hour at 55⁰C, rehydrated through a graded ethanol series and distilled water, immersed in PBS, and then treated with 0.1% trypsin solution in Tris buffer for 30 min at 37⁰C. Endogenous peroxidase was blocked with 10% normal serum. CD43, B220, and VpreBl (CD179a) antibodies (BD PharMingen) were used as primary antibodies. Secondary antibodies and diaminobenzidine were added according to the manufacturer's instruction. [000100] Results

[000101] The bodies and spleens of transgenic mice were enlarged relative to the spleens of wild-type mice (FIGS. 4A, 4B), with a spleen weight/body weight ratio three to four times greater than the ratio of wild-type mice (Table 1). Interestingly, the ratio did not vary much with age. [000102] Table 1. Spleen and body measurements for transgenic and wild-type mice.

[000103] *BW, body weight in grams (gr); **SW, spleen weight in milligrams (mg); *** WI, weight index (ratio of weight trangenic to wild-type) in milligrams per gram (mg/g); tg, transgenic mice; wt, wild-type mice.

[000104] The white blood cell count (WBC) of 3-month-old transgenic mice was 10 X 10⁶ ± 1 X 10⁶ per ml of peripheral blood, compared with 40 X 10⁶ ± 1.5 X 10⁶ per ml of peripheral blood for normal, age-matched mice. The WBC for transgenic mice at 6 months of age was even lower, with a value of 6 X 10⁶ ± 0.5 X 10⁶ per ml of peripheral blood compared with an unchanged value of 40 X 10⁶ ± 1.5 X 10⁶ per ml of peripheral blood for wild-type, age-matched mice.

[000105] Histopathology of the spleens (hematoxylin/eosin stain) of 3-week-old transgenic mice featured a consistent atypical lymphoid population invading and expanding the red pulp. The germinal follicles were unaffected, and there were multiple foci of secondary hematopoiesis (FIG. 5A). Histologically, mice at 6 months of age presented a greatly increased malignant lymphoid population with marked atypia and blastic appearance, proliferating in the vascular channels of the red pulp and gradually replacing the white pulp. The number of germinal follicles was decreased, and the overall architecture of the spleen was distorted by lymphoid proliferation (FIG. 5B). A histologically-similar lymphoid population was present in the bone marrow of 6-month-old mice. Expression of the proliferation antigen, Ki67, showed a marked lymphoid proliferation in transgenic mice (FIG. 5D), which was not observed in wild-type mice.

[000106] Immunohistochemical analysis of lymphoid proliferation in the transgenic spleens showed low positivity of the atypical expanded lymphocytes for B220 and VpreBl (CD 179a), although CD43 was negative (data not shown). IgM staining of paraffin- embedded sections of the spleens of transgenic mice showed the presence of μ chains in the cytoplasm of the proliferating lymphocytes (FIG. 6). In contrast, flow cytometry analysis failed to identify the expression of IgM on the surface of these cells, indicating that the expanded lymphoid cells expressed cytoplasmic μ chain, but did not express surface IgM.

[000107] Flow cytometry analysis, performed on single-cell suspensions of WBC from the spleens and bone marrow of transgenic and wild-type mice at ages of 3, 6, or 7 weeks, or 6 months, showed an increase in the number of B220^low/CD19^low/CD10^low/ IgM7TCR7CD43- lymphoid cells in both spleen and bone marrow in the transgenic mice, compared with their wild-type counterparts. This phenotype resembles the phenotype of proliferating lymphocytes observed in human acute lymphoblastic leukemia or lymphoblastic lymphoma. These findings indicate that the B220^|OW/CD19^l0W/CDl 0^l0w/ IgM7TCR7CD43- lymphoid population in the spleens of transgenic mice at 3 weeks of age is 9% of the entire gated lymphoid population as compared to only 1.65% in the spleens of wild type mice (assessed on one transgenic and one wild-type mouse). At 6 weeks of age, these percentages become 6.6 ± 1.4% in the spleen of transgenic mice and 4.7 ± 0.3% for mice at 7 weeks of age, while remaining unchanged in wild-type spleens (two transgenic mice analyzed from two different founding lines and two wild-type mice).

[000108] In the bone marrow of 6-month-old transgenic mice, we found an increase of the pre-B cell population as defined by B220^low/IgM^" expression, compared with wild type (FIGS. 7 and 8). Forward-scatter analysis of the B220^low/IgM^" cell population showed that these cells are large blastoid cells (data not shown). [000109] Based on the flow cytometry, histological and immunohistochemical analyses, it was concluded that a pre-B cell proliferation, defined as B220^low/CD19^low/CD10^low/IgM^' /TCR7CD43^", occurred in the spleens and bone marrows of transgenic mice and was already detectable at 3 weeks of age. This proliferation eventually resulted in splenomegaly, bone marrow replacement, and marked lymphopenia, features often associated with high-grade B cell malignancies. Consistent with this characterization, all of the transgenic mice developed high-grade B cell neoplasms by the age of 6 months (seven of seven transgenic mice) compared with the wild-type controls, which were all healthy (11 of 11 wild-type mice). Notably, the transgenic mouse line that did not overexpress miR155 was also normal.

[000110] Example 3: Cytogenetic analysis of Eμ-mmu-miR155 transgenic mice.

[0001 11] Materials and Methods

[000112] Cytogenetics:

[000113] Femur bone marrow was flushed with RPMI medium 1640/20% FBS and collected into 5 ml of RPMΪ medium 1640/20% FBS with 1% heparin. Cells were grown and assessed for chromosomal deletions, translocations, inversions, and number of metaphases using standard cytological techniques.

[000114] Ig Heavy Chain Rearrangements:

[000115] A probe was designed by amplifying a sequence in the JH4 fragment of the Ig heavy chain region of mouse genomic DNA using the following oligonucleotide primers: forward, 5 '-TG AAGG ATCTGCC AG AACTGAA-3' (SEQ ID NO:3)₅ and reverse, 5'- TGCAATGCTCAGAAAACTCCAT-S¹ (SEQ ID NO:4).

[000116] Spleens of the transgenic and wild-type mice were dissociated between frosted slides in PBS, treated with ammonium chloride to lyse erythrocytes, centrifuged, and resuspended in PBS. DNA was extracted from white blood cells of the spleens and digested with EcoRJ, Stul, BgIII, BamHI, and HindIIL Digested DNA was blotted on a Hybond N⁺ membrane, hybridized with the JH4 probe, which was radioactively labeled with γ-³²P, and then exposed to a Phosphorlmager screen and processed using a Typhoon scanner.

[000117] Results

[000118] Cytogenetic studies of the karyotype of splenocytes failed to identify consistent chromosomal abnormalities in spleens from transgenic mice compared with the spleens from normal littermates. However, some genomic alterations were observed occassionally (FIG. 9; see arrow). These results indicate that the expanded population of pre-B cells is diploid and cytogenetically quasinormal.

[000119] To detect clonality, Southern blot analysis was performed on splenocyte DNA from mice between 3 and 6 weeks of age using multiple digestion enzymes to assess V(D)J rearrangements. The presence of rearranged bands in transgenic mice relative to wild-type mice were not detected (FIG. 10), with the exception of one transgenic mouse, which had a consistent rearranged band on Southern blots performed with each of the different restriction enzymes (data not shown). These data indicated that the B cell population in mice of this age was, for the most part, polyclonal, at least until 6 weeks of age. Because the majority of malignancies are monoclonal, this finding suggests that miR155 could be the downstream target of signal transduction pathways activated in cancer.

[000120] Interestingly, overexpression of miR155 has been observed in solid tumors, such as breast and colon cancer, as well as lung cancers, where overexpression of miR155 was an indicator of poor prognosis (Volinia, S., et al., Proc. Natl. Acad. Sci. USA 103:2257- 2261 (2006)).

[000121] Example 4: Microarray expression profiling reveals up-regulation of VpreB 1 mRNA and other targets

[000122] Materials and Methods

[000123] RNA isolation:

[000124] Total RNA isolation was performed with the TRIzol reagent (Invitrogen), according to the manufacturer's instructions.

[000125] miRNA Expression Profiling:

[000126] RNA labeling and hybridization on miRNA microarray chips were performed as described (Liu, C.G., et al, Proc. Natl. Acad. ScL USA 101:9740-9744). Briefly, 5 μg of total RNA from each sample were labeled with biotin by reverse transcription using 5' biotin end- labeled random octamer oligonucleotide primers. Hybridization of biotin- labeled cDNA was carried out on a miRNA microarray chip (Ohio State University, Ver. 2.0), which contains 800 miRNA probes, including 245 human and 200 mouse miRNA genes, in quadruplicate. Hybridization signals were detected by binding of a Streptavidin- Alexa647 conjugate to biotin using Axon Scanner 4000B (Axon Instruments, Union City, CA). The images were quantified by GENEPIX 6.0 software (Axon Instruments).

[000127] mRNA Expression Profiling: [000128] GeneChip Mouse genome 430 2.0 arrays (Affymetrix), containing probe sets for greater than 45,000 characterized genes and expressed sequence tags, were used. Sample labeling and processing, GeneChip hybridization, and scanning were performed according to Affymetrix protocols. Briefly, double-stranded cDNA was synthesized from total RNA using the Superscript Choice System (Invitrogen), which adds a T7 RNA polymerase promoter site to the 3'-end (Genset, La Jolla, CA). Biotinylated cRNAs were generated from cDNAs in vitro and amplified using the BioArray T7 RNA polymerase labeling kit (Enzo Diagnostics). After purification of cRNAs using the RNeasy mini kit (Qiagen, Hilden, Germany), 20 μg of cRNA was fragmented at 94⁰C for 35 min. Approximately 12.5 μg of fragmented cRNA was used in a 250-μl hybridization mixture containing herring-sperm DNA (0.1 mg/ml; Promega), plus bacterial and phage cRNA controls (1.5 pM BioB, 5 pM BioC, 25 pM BioD, and 100 pM Cre) to serve as internal controls for hybridization efficiency. Aliquots (200 μl) of the mixture were hybridized to arrays for 18 hours at 45°C in a GeneChip Hybridization Oven 640 (Affymetrix). Each array was washed and stained with streptavidin— phycoerythrin (Tnvitrogen) and amplified with biotinylated antistreptavidin antibody (Vector Laboratories) on the GeneChip Fluidics Station 450 (Affymetrix). Arrays were scanned with the GeneArray G7 scanner (Affymetrix) to obtain image and signal intensities.

[000129] Results

[000130] Microarray analysis was performed on total RNA extracted from the splenic white blood cells of five transgenic mice, including one mouse that did not express the miR155 transgene, and the white blood cells of six wild-type littermate counterparts. The analysis revealed a 10- to 20-fold increase in the expression ofmiR155, miR194, miR224, miR217, and miR151 (Table 3), and a 2- to 3-fold decrease in the expression of miR146 and miR138, in transgenic mice that overexpress miR155, relative to the wild-type littermate control mice (data not shown). Using an Affymetrix microarray chip, the differential expression of mRNAs in the same group of transgenic mice was studied and compared with mRNA expression in the littermate controls. The statistical analysis of the Affymetrix microarray data showed that 200 proliferation-associated genes were up- regulated, whereas 50 genes were down-regulated in the miR155-overexpressing mice (Table 3). Notably, VpreBl mRNA was upregulated, which is expected to occur when the proliferation of pre-B cells takes place. These data complement the data from flow cytometry analysis and immunohistochemistry. 131] Table 2. Affymetrix microarray data for miR155 transgenic/wild-type mouse classification based on Prediction Analysis of Microarrays (PAM). mirl55

Name Probe Set D> Gene Title score wt score

1456609 at 1456609 at RIKEN cDNA 1810006K23 gene 0.8041 * -0.5744

1452324 at 1452324 at plasmacytoma variant translocation 1 0.4468 * -0.3192 glycoprotein 2 (zymogen granule

1449452 a at 1449452 a at membrane) 0.3377 * -0.2412

1459923 at 1459923 at brain expressed, X-linked 6 0.319 * -0.2279

1449222 at 1449222 at Epstein-Barr virus induced gene 3 0.31 * -0.2214

ATP-binding cassette, sub-family G

1424437 s at 1424437 s at (WHITE), member 4 0.2723 * -0.1945

1425784 a at 1425784 a at olfactomedin 1 0.2717 * -0.1941

1436827 at 1436827 at gene model 944, (NCBI) 0.2537 * -0.1812

1425677 a at 1425677 a at ankyrin 1, erythroid 0.2513 * -0.1795 solute carrier family 6 (neurotransmitter transporter,

1417636 at 1417636 at glycine), member 9 0.2476 * -0.1769

1441054 at 1441054 at apolipoprotein L, 2 0.233 * -0.1664 killer cell lectin-like receptor family

1458642 at 1458642 at E member 1 0.2307 * -0.1648 phospholipase A2, group IVA

1448558 a at 1448558 a at (cytosolic, calcium-dependent) 0.2157 * -0.154 aldehyde dehydrogenase family 1,

1418601 at 1418601 at subfamily A7 0.2136 * -0.1526

1458667 at 1458667 at RIKEN cDNA 4930519N13 gene 0.2084 * -0.1488

KDEL (Lys-Asp-Glu-Leu)

1436443 a at 1436443 a at containing 1 0.2073 * -0.1481

1416740 at 1416740 at procollagen, type V, alpha 1 0.2025 * -0.1447 origin recognition complex, subunit

1422663 at 1422663 at 1-like (S.cereviaiae) 0.2019 * -0.1442

1433892 at 1433892 at sperm associated antigen 5 0.1988 * -0.142 similar to RIKEN cDNA

1435660 at 1435660 at 5830484A20 0.1979 * -0.1413

1454622 at 1454622 at solute carrier family 38, member 5 0.1847 * -0.132

1426802 at 1426802 at septin 8 0.1821 * -0.13

1449869 at 1449869 at pre-B lymphocyte gene 1 (VpreBl) 0.1798 * -0.1284

1426015 s at 1426015 s at aspartate-beta-hydroxylase 0.1768 * -0.1263

1418710 at 1418710 at CD59a antigen 0.1697 * -0.1212

1437244 at 1437244 at Growth arrest-specific 2 like 3 0.1662 * -0.1187

1429830 a at 1429830 a at CD59a antigen 0.1651 * -0.118

ATP-binding cassette, sub-family B

1422524 at 1422524 at (MDR/TAP), member 6 0.1604 * -0.1145

1435287 at 1435287 at adducin 2 (beta) 0.158 * -0.1129

1436984 at 1436984 at abl-interactor 2 0.1554 * -0.111

1453226 at 1453226 at RlKEN cDNA 3000004C01 gene 0.1467 * -0.1048

1429146 at 1429146 at RIKEN cDNA 6620401M08 gene 0.139 * -0.0993 1454630 at 1454630 at cDNA sequence BC034054 0.1385 * -0.099

1429089 s at 1429089 s at RIKEN cDNA 2900026A02 gene 0.138 * -0.0986

1455980 a at 1455980 a at Growth arrest-specific 2 like 3 0.1375 * -0.0982

1427677 a at 1427677 a at SRY-box containing gene 6 0.1363 * -0.0974

1419031 at 1419031 at fatty acid desaturase 2 0.1338 * -0.0956

1422016 a at 1422016 a at centromere autoantigen H 0.1309 * -0.0935 immunoglobulin lambda-like

1420176 x at 1420176 x at polypeptide 1 0.1305 * -0.0932

1434501 at 1434501 at — 0.1246 * -0.089

1419665 a at 1419665 a at nuclear protein 1 0.123 * -0.0878

1446391 at 1446391 at Synuclein, alpha 0.1203 * -0.0859

1419421 at 1419421 at ankyrin l, erythroid 0.1181 * -0.0844 peptidylprolyl isomerase

1452458 s at 1452458 s at (cyclophilin) like 5 0.1163 * -0.0831

1417939 at 1417939 at RAD51 associated protein 1 0.1149 * -0.0821

1436725 at 1436725 at RIKEN cDNA E130306D19 gene 0.1104 * -0.0789

1437187 at 1437187 at E2F transcription factor 7 0.1103 * -0.0788

1453004 at 1453004 at RIKEN cDNA 3110004L20 gene 0.1062 * -0.0758

TPX2, microtubule-associated

1428105 at 1428105 at protein homolog (Xenopus laevis) 0.1049 * -0.0749

1448926 at 1448926 at homeo box A5 0.1047 * -0.0748

1437370 at 1437370 at shugoshin-like 2 (S. pombe) 0.1046 * -0.0747

1430999 a at 1430999 a at short coiled-coil protein 0.1038 * -0.0742.

DNA segment, Chr 12, ERATO Doi

1454757 s at 1454757 s at 647, expressed 0.1018 * -0.0727

1418026 at 1418026 at exonuclease 1 0.1016 * -0.0726

ATPase, Na+/K+ transporting, beta 2

1435148 at 1435148 at polypeptide 0.1012 * -0.0723

1434553 at 1434553 at RIKEN cDNA 4930577M16 gene 0.1009 * -0.0721

1422967 a at 1422967 a at transferrin receptor 0.1008 * -0.072

1434479 at 1434479 at expressed sequence AI413331 0.1001 * -0.0715

1431893 a at 1431893 a at trans-prenyltransferase 0.0994 * -0.071

1447655 x at 1447655 x at SRY-box containing gene 6 0.0959 * -0.0685

1434789 at 1434789 at DEP domain containing IB 0.095 * -0.0678 phosphate cytidylyltransferase 1 ,

1421957 a at 1421957 a at choline, alpha isoform 0.0946 * -0.0676

Wolf-Hirschhorn syndrome

1455228 at 1455228 at candidate 1 (human) 0.0937 * -0.0669

1435663 at 1435663 at estrogen receptor 1 (alpha) 0.093 * -0.0664

1429058 at 1429058 at RIKEN cDNA 1110004B 13 gene 0.0925 * -0.0661 dual-specificity tyrosine-(Y)-

1424229 at 1424229 at phosphorylation regulated kinase 3 0.0919 * -0.0657 intercellular adhesion molecule 4,

1422930 at 1422930 at Landsteiner-Wiener blood group 0.0917 * -0.0655

1452591 a at 1452591 a at RIKEN cDNA 2410018G20 gene 0.0905 * -0.0646

1453416 at 1453416 at growth arrest-specific 2 like 3 0.0886 * -0.0633

1433908 a at 1433908 a at cortactin 0.0874 * -0.0624 1419595 a at 1419595 a at gamma-glutamyl hydrolase 0.0872 * -0.0623

1421654 a at 1421654 a at lamin A 0.0867 * -0.062

1417323 at 1417323 at RIKEN cDNA 5430413102 gene 0.085 * -0.0607 myeloid ecotropic viral integration

1450992 a at 1450992 a at site 1 0.0832 * -0.0594

1435773 at 1435773 at RIKEN cDNA 4930547N16 gene 0.0829 * -0.0592

1438711 at 143871 1 at — 0.0829 * -0.0592

1429701 at 1429701 at RIKEN cDNA 2410003 J06 gene 0.0827 * -0.0591

1433582 at 1433582 at RIKEN cDNA 1190002N15 gene 0.0823 * -0.0588

1460192 at 1460192 at oxysterol binding protein-like IA 0.0817 * -0.0584

ATP-binding cassette, sub-family C

1443870 at 1443870 at (CFTR/MRP), member 4 0.0814 * -0.0581

SH3 domain and tetratricopeptide

1456020 at 1456020 at repeats 2 o;o8i3 * -0.0581 killer cell lectin-like receptor subfamily A, member 12 /// killer cell lectin-like receptor, subfamily A. member 4 /// killer cell lectin-like receptor, subfamily A₅ member 7 /// killer cell lectin-like receptor subfamily A, member 20 /// killer cell lectin-like receptor, subfamily A.

1451664 x at 1451664 x at member 18 0.0812 * -0.058

1421975 a at 1421975 a at adducin 2 (beta) 0.0805 * -0.0575

1423124 x at 1423124 x at RAD54 like (S. cerevisiae) 0.0789 * -0.0563

1417749 a at 1417749 a at tight junction protein 1 0.0779 * -0.0557

1425145 at 1425145 at interleukin 1 receptor-like 1 0.0768 * -0.0549

1424722 at 1424722 at RIKEN cDNA 1300017J02 gene 0.0762 * -0.0544

1455409 at 1455409 at spire homolog 1 (Drosophila) 0.0739 * -0.0528

1453067 at 1453067 at RIKEN cDNA 2610040C18 gene 0.0734 * -0.0524

1430839 at 1430839 at RIKEN cDNA 9430076G02 gene 0.0713 * -0.0509

1434577 at 1434577 at cDNA sequence BC052040 0.0704 * -0.0503

Polymerase (DNA directed), epsilon

1457306 at 1457306 at 3 (pi 7 subunit) 0.0699 * -0.0499

1429734 at 1429734 at RIKEN cDNA 4632434111 gene 0.0695 * -0.0496

1449060 at 1449060 at kinesin family member 2C 0.0684 * -0.0489

1424223 at 1424223 at RIKEN cDNA 1700020C11 gene 0.0676 * -0.0483

1428372 at 1428372 at suppression of tumorigenicity 5 0.0667 * -0.0476 phosphate cytidylyltransferase 1,

1436124 at 1436124 at choline, beta isoform 0.0663 * -0.0474

1417656 at 1417656 at myeloblastosis oncogene-like 2 0.0661 * -0.0472

1436922 at 1436922 at — 0.0657 * -0.047

1455009 at 1455009 at carboxypeptidase D 0.065 * -0.0464

1434826 at 1434826 at expressed sequence AI256775 0.064 * -0.0457

1455746 at 1455746 at kinesin family member 13 A 0.0628 * -0.0449

1419087 s at 1419087 s at splicing factor 3a, subunit 1 0.0616 * -0.044

1418919 at 1418919 at shugoshin-like 1 (S. pombe) 0.0611 * -0.0436 DnaJ (Hsp40) homolog, subfamily C

1433596 at 1433596 at member 6 0.061 * -0.0436

1430538 at 1430538 at RIKEN cDNA 2210013O21 gene 0.0605 * -0.0432

1454193 at 1454193 at RIKEN cDNA 5430401H09 gene 0.0605 * -0.0432 ependymin related protein 2

1450380 at 1450380 at (zebrafish) 0.06 * -0.0428

1434322 at 1434322 at RIKEN cDNA A930021H16 gene 0.0596 * -0.0426 gap junction membrane channel

1438650 x at 1438650 x at protein alpha 1 0.0593 * -0.0424

1451914 a at 1451914 a at adducin 2 (beta) 0.0574 * -0.041

1436584 at 1436584 at sprouty homolog 2 (Drosophila) 0.0555 * -0.0396

1455012 s at 1455012 s at tripartite motif protein 37 0.0551 * -0.0394

1452026 a at 1452026 a at phospholipase A2, group XIIA 0.0524 * -0.0374 acyl-CoA synthetase long-chain

1451257 at 1451257 at family member 6 0.0521 * -0.0372

1435792 at 1435792 at component of SplOO-rs 0.0513 * -0.0366

1435029 at 1435029 at RIKEN cDNA B230120H23 gene 0.0492 * -0.0351

1434630 at 1434630 at ankyrin repeat domain 28 0.0491 * -0.0351

1426801 at 1426801 at septin 8 0.0483 * -0.0345

1436936 s at 1436936 s at inactive X specific transcripts 0.0458 * -0.0327

1418069 at 1418069 at apolipoprotein C-II 0.0456 * -0.0326

CCR4 carbon catabolite repression 4

1425837 a at 1425837 a at like (S. cerevisiae) 0.0456 * -0.0326

1441757 at 1441757 at RIKEN cDNA 1190002F15 gene 0.0454 * -0.0325

ATP-binding cassette, sub-family G

1422906 at 1422906 at (WHITE), member 2 0.045 * -0.0322

1454858 x at 1454858 x at RIKEN CDNA 3300001H21 gene 0.045 * -0.0321

1443673 x at 1443673 x at — 0.0449 * -0.032

1417587 at 1417587 at timeless homolog (Drosophila) 0.0447 * -0.0319 homeodomain interacting protein

1456022 at 1456022 at kinase 2 0.0445 * -0.0318

1438202 at 1438202 at RIKEN cDNA C920005C14 gene 0.0439 * -0.0314

1453836 a at 1453836 a at monoglyceride lipase 0.0434 * -0.031

1422966 a at 1422966 a at transferrin receptor 0.0431 * -0.0308 checkpoint kinase 1 homolog (S.

1439208 at 1439208 at pombe) 0.0423 * -0.0302

1422944 a at 1422944 a at diaphanous homolog 3 (Drosophila) 0.0417 * -0.0298

1419412 at 1419412 at chemokine (C motif) Iigand 1 0.0414 * -0.0296

1435378 at 1435378 at RIKEN cDNA 2210020M01 gene 0.0414 * -0.0296

1422788 at 1422788 at solute carrier family 43, member 3 0.0413 * -0.0295 non imprinted in Prader- Willi/Aπgelman syndrome 1

1452763 at 1452763 at homolog (human) 0.0413 * -0.0295

1428369 s at 1428369 s at Rho GTPase activatingj>rotein 21 0.0409 * -0.0292 forkhead box Ml /// phosphatidylethanolamine binding

1453107 s at 1453107 s at protein /// RIKEN cDNA 0.0404 * -0.0288 subfamily K, member 1

1442000 at 1442000 at similar to novel protein 0.0222 * -0.0158

CTFl 8, chromosome transmission Fidelity factor 18 homoiog (S.

1452098 at 1452098 at cerevisiae) 0.0219 * -0.0156

1453049 at 1453049 at RTKEN cDNA 6620401M08 gene 0.0217 * -0.0155 noπ imprinted in Prader- Willi/Angelman syndrome 1

1434864 at 1434864 at homoiog (human) 0.0212 * -0.0152

1460495 s at 1460495 s at protease, serine, 25 0.021 * -0.015

1453181 x at 1453181 x at phospholipid scramblase 1 0.0209 * -0.0149

C-type lectin domain family 4,

1420330 at 1420330 at member e 0.0208 * -0.0149 phosphate cytidylyltransferase 1,

1438011 at 1438011 at choline, alpha isoform 0.0205 * -0.0146 prostaglandin E receptor 3 (subtype

1450344 a at 1450344 a at EP3) 0.0204 * -0.0146

G-protein signalling modulator 2

1424895 at 1424895 at (AGS3-like, C. elegans) 0.0201 * -0.0144

1426543 x at 1426543 x at RIKEN cDNA 2310067E08 gene 0.0193 * -0.0138

1423878 at 1423878 at glycophorin C 0.0186 * -0.0133

1427263 at 1427263 at inactive X specific transcripts 0.0186 * -0.0133

RIKEN cDNA 3300001H21 gene ///

1434150 a at 1434150 a at UbiE-YGHLl fusion protein 0.0185 * -0.0132

1453681 at 1453681 at ATPase inhibitory factor 1 0.0181 * -0.013

1450556 at 1450556 at spectrin beta 1 0.0175 * -0.0125

1434554 at 1434554 at tripartite motif protein 37 0.0174 * -0.0124

1448529 at 1448529 at thrombomodulin 0.0173 * -0.0123

1429404 at 1429404 at RIKEN cDNA 2010317E24 gene 0.0168 * -0.012

1432886 at 1432886 at RIKEN cDNA 5730488B01 gene 0.0162 * -0.0116

1435325 at 1435325 at ubiquitin specific protease 46 0.016 * -0.0114

1434587 x at 1434587 x at phosphatidylserine synthase 2 0.0157 * -0.0112

1418003 at 1418003 at RIKEN cDNA 1190002H23 gene 0.0156 * -0.0111 bone morphogenic protein receptor,

1434310 at 1434310 at type II (serine/threonine kinase) 0.0147 * -0.0105

RNA (guanine-9-) methyltransferase

1435035 at 1435035 at domain containing 2 0.0144 * -0.0103

1424413 at 1424413 at opioid growth factor receptor-like 1 0.014 * -0.01 transforming, acidic coiled-coil

1436872 at 1436872 at containing protein 3 0.0133 * -0.0095

1417878 at 1417878 at E2F transcription factor 1 0.013 * -0.0093 homeodomain interacting protein

1428433 at 1428433 at kinase 2 0.0125 * -0.0089

ANl, ubiquitin-like, homoiog

1429642 at 1429642 at (Xenopus laevis) 0.0122 * -0.0087

1435786 at 1435786 at kelch-Hke 12 (Drosophila) 0.0119 * -0.0085

RAB3A interacting protein (rabin3)-

1428391 at 1428391 at like l 0.0118 * -0.0085 1451596 a at 1451596 a at sphingosine kinase 1 0.0117 * -0.0084

1422619 at 1422619 at phosphatidic acid phosphatase 2a 0.0111 * -0.0079 checkpoint kinase 1 homolog (S.

1449708 s at 1449708 s at pombe) 0.0106 * -0.0076 thyroid hormone receptor interactor

1429294 at 1429294 at 13 0.0105 * -0.0075

1450862 at 1450862 at RAD54 like (S. cerevisiae) 0.0103 * -0.0074

1433695 at 1433695 at RIKEN cDNA 1500041B16 gene 0.0097 * -0.0069

1451083 s at 1451083 s at alanyl-tRNA synthetase 0.0097 * -0.0069

1422620 s at 1422620 s at phosphatidic acid phosphatase 2a 0.0094 * -0.0067

1457722 at 1457722 at RIKEN cDNA A630024B12 gene 0.0091 * -0.0065 proline-serine-threonine

1455405 at 1455405 at phosphatase-interacting protein 2 0.009 * -0.0064

1460010 a at 1460010 a at phosphatidylserine synthase 2 0.0089 * -0.0063

1424412 at 1424412 at opioid growth factor receptor-like 1 0.0083 * -0.0059 protein kinase, cAMP dependent

1456475 s at 1456475 s at regulatory, type II beta 0.0082 * -0.0058

1449714 at 1449714 at RIKEN cDNA 5730472N09 gene 0.0077 * -0.0055

1434645 at 1434645 at RIKEN cDNA C530008M17 gene 0.0069 * -0.005

1425157 x at 1425157 x at RIKEN cDNA 1300010A20 gene 0.0067 * -0.0048

1432273 a at 1432273 a at Duffy blood group 0.0063 * -0.0045 origin recognition complex, subunit

1417037 at 1417037 at 6-like (S. cerevisiae) 0.0062 * -0.0044 zinc finger, CCHC domain

1428402 at 1428402 at containing 3 0.0062 * -0.0044

1416130 at 1416130 at prion protein 0.0061 * -0.0043

1455218 at 1455218 at RIKEN cDNA 6330503K22 gene 0.0056 * -0.004

1452166 a at 1452166 a at keratin complex I, acidic, gene 10 0.0049 * -0.0035 gap junction membrane channel

1437992 x at 1437992 x at protein alpha 1 0.0037 * -0.0026

1449015 at 1449015 at resistin like alpha 0.0033 * -0.0023

1428713 s at 1428713 s at RIKEN cDNA 4833427B12 gene 0.0032 * -0.0023

1427105 at 1427105 at RIKEN cDNA 261051 OJl 7 gene 0.0031 * -0.0022

1426541 a at 1426541 a at RIKEN cDNA 2310067E08 gene 0.0028 * -0.002

1424293 s at 1424293 s at RIKEN cDNA 2610319K07 gene 0.0024 * -0.0017

1423724 at 1423724 at ZWlO interactor 0.002 * -0.0014

1451609 at 1451609 at RIKEN cDNA 1300010A20 gene 0.0018 * -0.0013 solute carrier family 19 (thiamine

1417902 at 1417902 at transporter), member 2 0.0016 * -0.0012

1424292 at 1424292 at DEP domain containing Ia 0.0015 * -0.0011

1455983 at 1455983 at cell division cycle associated 2 0.0015 * -0.0011

ATPase, H+ transporting, lysosomal -9.00E-

1448211 at 1448211 at VO subunit E isoform 2 0.0013 * 04

-9.00E-

1453769 at 1453769 at RIKEN cDNA 2610318C08 gene 0.0012 * 04 sirtuin 3 (silent mating type 6.00E-04 -4.00E-

1417892 a at 1417892 a at information regulation 2, homolog) 3 * 04 1456440 s at 1456440 s at Transcribed locus -0.0117 # 0.0084

1454742 at 1454742 at RasGEF domain family, member IB -0.0122 # 0.0087 suppressor of fused homolog

1450024 at 1450024 at (Drosophila) -0.0125 # 0.009

1433953 at 1433953 at zinc finger protein 277 -0.0135 # 0.0096 eukaryotic translation initiation factor 2, subunit 3, structural gene Y-

1417210 at 1417210 at linked -0.0137 # 0.0098

Protein phosphatase 2, regulatory

1444828 at 1444828 at subunit B (B56), gamma isoform -0.0139 # 0.0099

1447502 at 1447502 at — -0.014 # 0.01

1422445 at 1422445 at integrin alpha 6 -0.0148 # 0.0106

1453244 at 1453244 at RIKEN cDNA 5830416P10 gene -0.0157 # 0.0112

E26 avian leukemia oncogene 1, 5'

1426725 s at 1426725 s at domain -0.0175 # 0.0125

1438577 at 1438577 at Transcribed locus -0.018 # 0.0129

DEAD (Asp-Glu-Ala-Asp) box

1452077 at 1452077 at polypeptide 3, Y-linked -0.02 # 0.0143 special AT-rich sequence binding

1416007 at 1416007 at protein 1 -0.0203 # 0.0145

DEAD (Asp-Glu-Ala-Asp) box

1426438 at 1426438 at polypeptide 3, Y-linked -0.021 # 0.015

Fc receptor, IgE, low affinity II,

1422122 at 1422122 at alpha polypeptide -0.0213 # 0.0152

1434260 at 1434260 at FCH and double SH3 domains 2 -0.0215 # 0.0153

1417816 s at 1417816 s at tumor differentially expressed 1 -0.0222 # 0.0158

T cell receptor associated

1427532 at 1427532 at transmembrane adaptor 1 -0.0222 # 0.0159

1454947 a at 1454947 a at cDNA sequence BC002236 -0.0224 # 0.016

1418235 at 1418235 at autophagy-related 5-like (yeast) -0.0243 # 0.0173

1418353 _at 1418353 at CD5 antigen -0.0258 # 0.0184

1450262 at 1450262 at cardiotrophin-like cytokine factor 1 -0.026 # 0.0186

1455165 at 1455165 at Transcribed locus -0.0268 # 0.0191

1439595 at 1439595 at T-cell receptor alpha chain -0.0272 # 0.0194 .

1426620 at 1426620 at carbohydrate sulfotransferase 10 -0.0278 # 0.0198

1454745 at 1454745 at Rho GTPase activating protein 29 -0.029 # 0.0207

1439719 at 1439719 at RIKEN cDNA E430004N04 gene -0.0292 # 0.0208

1435374 at 1435374 at Transcribed locus -0.0302 # 0.0216

1456678 at 1456678 at RIKEN cDNA 1700091G21 gene -0.0306 # 0.0218

1423176 at 1423176 at transducer of ErbB-2.1 -0.0348 # 0.0249

1424374 at 1424374 at GTPase, IMAP family member 4 -0.0355 # 0.0253

1446614 at 1446614 at Diacylglycerol kinase zeta -0.0359 # 0.0257

1448862 at 1448862 at intercellular adhesion molecule 2 -0.0365 # 0.0261

ATPase, Na+/K+ transporting, beta 1

1439036 a at 1439036 a at polypeptide -0.0375 # 0.0268

1442023 at 1442023 at RIKEN cDNA A530030E21 gene -0.0376 # 0.0269

1436182 at 1436182 at special AT-rich sequence binding -0.0385 # 0.0275 protein 1

1443703 at 1443703 at Transcribed locus -0.0385 # 0.0275

1422562 at 1422562 at Ras-related associated with diabetes -0.0396 # 0.0283

1454893 at 1454893 at RIKEN cDNA 1110013L07 gene -0.0402 # 0.0287

1427831 s at 1427831 s at zinc finger protein 260 -0.0404 # 0.0289

E26 avian leukemia oncogene 1, 5'

1452163 at 1452163 at domain -0.0417 # 0.0298

1421570 at 1421570 at interleukin 9 receptor -0.0431 # 0.0308

1442998 at 1442998 at Cytidine 5'-triphosphate synthase 2 -0.0437 # 0.0312

RAB30, member RAS oncogene

1426452 a at 1426452 a at family -0.0473 # 0.0338 arsenic (+3 oxidation state)

1431980 a at 1431980 a at methyltransferase -0.0478 # 0.0341

1456205 x at 1456205 x at tubulin cofactor a -0.048 § 0.0343

1441041 at 1441041 at RlKEN cDNA 2810407L07 gene -0.0491 # 0.0351 hypoxia inducible factor I₅ alpha

1427418 a at 1427418 a at subunit -0.0492 # 0.0351 dual-specificity tyrosine-(Y)-

1456502 at 1456502 at phosphorylation regulated kinase 2 -0.0502 # 0.0358 chromodomain protein, Y

1432229 a at 1432229 a at chromosome-like 2 -0.0516 # 0.0368

1453726 s at 1453726 s at RlKEN cDNA 2810407C02 gene -0.0517 # 0.0369 ribosomal protein S6 kinase,

1440343 at 1440343 at polypeptide 5 -0.0519 # 0.037

1435584 at 1435584 at expressed sequence AI662791 -0.0522 # 0.0373

1419481 at 1419481 at selectin, lymphocyte -0.0524 # 0.0374

1437907 a at 1437907 a at tubulin cofactor a -0.0532 # 0.038

1419192 at 1419192 at interleukin 4 induced 1 -0.0554 # 0.0395

1424936 a at 1424936 a at dynein, axonemal, heavy chain 8 -0.0562 # 0.0402 coagulation factor II (thrombin)

1448931 at 1448931 at receptor-like 1 -0.0571 # 0.0408

ATPase, Na+/K+ transporting, beta 1

1423890 x at 1423890 x at polypeptide -0.0582 # 0.0415

Non-catalytic region of tyrosine

1458432 at 1458432 at kinase adaptor protein 2 -0.0588 # 0.042 similar to hypothetical protein

1440217 at 1440217 at FLJ39743 -0.0593 # 0.0424 signal-induced proliferation-

1440647 at 1440647 at associated 1 like 1 -0.0596 # 0.0426

1440284 at 1440284 at Transcribed locus -0.0598 # 0.0427

1457691 at 1457691 at Transcribed locus -0.0614 # 0.0439

1455256 at 1455256 at TRAF2 and NCK interacting kinase -0.0625 # 0.0447

1421628 at 1421628 at interleukin 18 receptor 1 -0.0635 # 0.0454

16 days neonate thymus cDNA, RIKEN full-length enriched library, clone: Al 30046K23 product:unknown EST, full insert

1442045 at 1442045 at sequence -0.0635 # 0.0453 1452737 at 1452737 at RIKEN cDNA 2810008M24 gene -0.0673 # 0.0481

1419480 at 1419480 at selectin, lymphocyte -0.0683 # 0.0488

1459632 at 1459632 at Cysteine-rich motor neuron 1 -0.0722 # 0.0516

1427359 at 1427359 at RIKEN cDNA A630082K20 gene -0.0757 # 0.0541

1426640 s at 1426640 s at tribbles homolog 2 (Drosophila) -0.0783 # 0.0559

DNA segment, Chr 6, Brigham &

1435754 at 1435754 at Women's Genetics 1452 expressed -0.0791 # 0.0565 cytoplasmic tyrosine kinase,

1460204 at 1460204 at Dscr28C related (Drosophila) -0.0803 # 0.0574

1454897 at 1454897 at RIKEN cDNA 6330509M05 gene -0.0804 # 0.0574

1449520 at 1449520 at expressed sequence AI428795 -0.0813 # 0.058

Rap guanine nucleotide exchange

1421622 a at 1421622 a at factor (GEF) 4 -0.0841 # 0.0601

1425245 a at 1425245 a at regulator of G-protein signaling 11 -0.0842 # 0.0602 special AT-rich sequence binding

1416008 at 1416008 at protein 1 -0.0847 # 0.0605

1452009 at 1452009 at RIKEN cDNA 9130422G05 gene -0.0861 # 0.0615

1445141 at 1445141 at inhibitor of kappaB kinase beta -0.0875 # 0.0625

1431169 at 1431169 at RIKEN cDNA D230012E17 gene -0.0878 # 0.0627

1443192 at 1443192 at RIKEN cDNA E430004N04 gene -0.0882 # 0.063

1428834 at 1428834 at dual specificity phosphatase 4 -0.091 # 0.065

1423989 at 1423989 at RIKEN cDNA 2210010N04 gene -0.0914 # 0.0653 poly (ADP-ribose) polymerase

1443573 at 1443573 at family, member 1 -0.0916 # 0.0654

1450061 at 1450061 at ectodermal-neural cortex 1 -0.0959 # 0.0685 bromodomain and WD repeat

1452503 a at 1452503 a at domain containing 1 -0.0969 # 0.0692

1451313 a at 1451313 a at RIKEN cDNA 1110067D22 gene -0.1008 # 0.072

1437253 at 1437253 at RIKEN cDNA A630054L15 gene -0.1009 # 0.072

1428726 at 1428726 at THUMP domain containing 2 -0.1017 # 0.0727

1451622 at 1451622 at LMBRl domain containing 1 -0.103 # 0.0736

1435456 at 1435456 at expressed sequence AI428795 -0.1035 # 0.0739

1444181 at 1444181 at GTPase, IMAP family member 5 -0.1036 # 0.074

1418762 at 1418762 at decay accelerating factor 1 -0.1059 # 0.0757

1423297 at 1423297 at adducin 3 (gamma) -0.1071 # 0.0765

Rap guanine nucleotide exchange

1425518 at 1425518 at factor (GEF) 4 -0.1071 # 0.0765 bromodomain and WD repeat

1427322 at 1427322 at domain containing 1 -0.1084 # 0.0775

1426158 at 1426158 at T-cell receptor beta, variable 13 -0.1126 # 0.0804

1416129 at 1416129 at RIKEN cDNA 1300002F13 gene -0.1139 # 0.0814

SIDl transmembrane family,

1426550 at 1426550 at member 1 -0.1143 # 0.0817

1428510 at 1428510 at latrophilin 1 -0.1187 # 0.0848

1456520 at 1456520 at RIKEN cDNA 9530033F24 gene -0.1202 # 0.0859

1419212 at 1419212 at icos ligand -0.126 # 0.09

1437540 at 1437540 at — -0.1261 # 0.0901 1429969 at 1429969 at RIKEN cDNA 4833403J16 gene -0.13 # 0.0929

Zinc finger, SWIM domain

1459722 at 1459722 at containing 6 -0.13 # 0.0928

1449642 at 1449642 at Epstein-Barr virus induced gene 2 -0.1319 # 0. 0942

1444283 at 1444283 at GTPase, IMAP family member 7 -0.1324 # 0. 0945

1434333 a at 1434333 a at protein kinase D2 -0.1329 # 0. 0949

1453119 at 1453119 at OTU domain containing 1 -0.1339 # 0. 0957 potassium channel, subfamily K₅

1421852 at 1421852 at member 5 -0.1385 # 0.099

1425186 at 1425186 at LMBRl domain containing 1 -0.1443 # 0. 103 heparan sulfate (glucosamine) 3-O-

1433977 at 1433977 at sulfotransferase 3Bl -0.1462 # 0. 1044

1436491 at 1436491 at RIKEN cDNA 5830431 AlO gene -0.1518 # 0. 1084

1460242 at 1460242 at decay accelerating factor 1 -0.1524 # 0 1088

16 days neonate thymus cDNA, RIKEN full-length enriched library, clone:A130006J10 product: unknown

1445277 at 1445277 at EST, full insert sequence -0.1527 # 0 1091

1418497 at 1418497 at fibroblast growth factor 13 -0.1588 # 0 1134

1455425 at 1455425 at expressed sequence BBOO 1228 -0.1632 # 0 1166 kynurenine 3-monooxygenase

1418998 at 1418998 at (kynurenine 3-hydroxylase) -0.1673 # 0 1195

1452167 at 1452167 at RIKEN cDNA 2810407C02 gene -0.1698 # 0 1213

1442266 at 1442266 at expressed sequence AI662175 -0.1713 # 0 1223 calcium/calmodulin-dependent

1439843 at 1439843 at protein kinase IV -0.1732 # 0 1237

T-cell receptor beta, variable 13 /// similar to TCRB V7S 1 /// similar to

1427752 a at 1427752 a at TCRB V7S1 -0.1805 # 0.1289

PX domain containing

1451253 at 1451253 at serine/threonine kinase -0.1819 # 0 .1299 brain expressed myelocytomatosis

1428669 at 1428669 at oncogene -0.1862 # 0 .133 zinc finger, SWIM domain

1434967 at 1434967 at containing 6 -0.1869 # 0 .1335 tumor necrosis factor receptor

1422231 a at 1422231 a at superfamily, member 25 -0.1906 # 0 .1361

1428914 at 1428914 at RIKEN cDNA 2310014Dl 1 gene -0.1917 # 0.1369

1434175 s at 1434175 s at RIKEN cDNA 2210010N04 gene -0.2013 # 0.1438

E26 avian leukemia oncogene 2, 3'

1416268 at 1416268 at domain -0.203 # 0 .145

1436851 at 1436851 at protein kinase Nl -0.2037 # 0 .1455

1438862 at 1438862 at RJKEN cDNA A630005I04 gene -0.2078 # 0 .1484

1448107 x at 1448107 x at kalHkrein 6 -0.2085 # 0 .149 ubiquitin-conjugating enzyme E2D

1424062 at 1424062 at 1, UBC4/5 homologjyeast) -0.2114 # 0 .151 lung-inducible neuralized-related

1444003 at 1444003 at C3HC4 RING domain protein -0.2133 # 0 .1524

[0132] The mirl55 mRNA signature: * indicates the genes that are over-expressed in mouse mirl55, # indicates the genes that are under-expressed. The score is the PAM score (Tibshirani, R. J., Hastie, T. J., Narasimhan, B., and Chu, G. (2002), "Diagnosis of multiple cancer types by shrunken centroids of gene expression," Proceedings of the National Academy of Sciences, 99, 6567-6572). PAM's method of "nearest shrunken centroids" identifies the subsets of genes that best characterize the mirl55 transgene. PAM's score is not a fold change.

[0132] Table 3. Affymetrix microarray data depicting signature of microRNAs that are significantly over-expressed in mirl55 transgenic mice based on Prediction Analysis of Microarrays (PAM) classification (5 transgenic mice and 6 wild-type mice).

Name miRlS5 score wt score mmu-mir-151 -prec 3.9218 * -2.2411 mmu-mir-217-precNo2 3.1565 * -1.8037 mmu-mir-224-precformerl75Mol 1.9286 * -1.1021 mmu-mir- 194-prec 1.6021 * -0.9155 mmu-mir-201 -prec 1.5653 * -0.8945 mmu-mir- 155-prec 1.4967 * -0.8553 mmu-mir-218-2-precNo2 0.939 * -0.5365 mmu-mir-182 -prec 0.4886 * -0.2792

The mirl55 microRNA signature: * indicates the microRNAs that are significantly over-expressed in Eμ-mmu-miR155 transgenic mice.

[0132] The relevant teachings of all publications cited herein that have not explicitly been incorporated by reference, are incorporated herein by reference in their entirety. While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

CLAIMS What is claimed is:

1. A transgenic non-human animal whose genome comprises a nucleic acid construct comprising at least one transcriptional regulatory sequence capable of directing expression in B cells of the animal, wherein said transcriptional regulatory sequence is operably linked to a nucleic acid encoding a miR155 gene product comprising a nucleotide sequence having at least 90% sequence identity to SEQ ID NO:1 and/or SEQ ID NO:2.

2. The transgenic non-human animal as in any of the preceding claims, wherein the at least one transcriptional regulatory sequence comprises a VH promoter.

3. The transgenic non-human animal as in any of the preceding claims, wherein the at least one transcriptional regulatory sequence comprises an Ig heavy chain-Eμ enhancer.

4. The transgenic non-human animal as in any of the preceding claims, wherein the nucleic acid encodes a miR155 gene product comprising SEQ ID NO:1 and/or SEQ ID NO:2.

5. The transgenic non-human animal as in any of the preceding claims, wherein the VH promoter is derived from mouse.

6. The transgenic non-human animal as in any of the preceding claims, wherein the Ig heavy chain-Eμ enhancer is derived from mouse.

7. The transgenic non-human animal as in any of the preceding claims, wherein the animal is a mouse.

8. The transgenic non-human animal as in any of the preceding claims, wherein the animal has an expanded population of B2201ow/CD191ow/CD101ow/ IgM-/TCR-/CD43- lymphoid cells in the spleen, the bone marrow or both, relative to a suitable control.

9. The transgenic non-human animal as in any of the preceding claims, wherein the animal exhibits a lymphoproliferative condition.

10. The transgenic non-human animal as in any of the preceding claims, wherein the lymphoproliferative condition is a B cell malignancy.

11. The transgenic non-human animal as in any of the preceding claims, wherein B cell malignancy is a leukemia, lymphoma or neoplasm.

12. The transgenic non-human animal as in any of the preceding claims, wherein the lymphoproliferative condition is a preleukemic state.

13. The transgenic non-human animal as in any of the preceding claims, wherein the animal exhibits an expanded population of B2201ow/CD191ow/CD101ow/ lgM-/TCR-/CD43- lymphoid cells, enlarged abdomen, splenomegaly, bone marrow replacement, lymphopenia and a combination thereof.

14. The transgenic non-human animal as in any of the preceding claims, wherein the nucleic acid construct comprises the 3' UTR and poly(A) sequence of the β-globin gene.

15. The transgenic non-human animal as in any of the preceding claims, wherein the B cell malignancy exhibits characteristics of human acute lymphoblastic leukemia, human lymphoblastic lymphoma or a combination thereof.

16. A transgenic non-human animal whose genome comprises a nucleic acid construct comprising a VH promoter and an Ig heavy chain-Eμ enhancer, operably linked to a nucleic acid encoding a miR155 gene product comprising SEQ ID NO:1 and/or SEQ ID NO:2.

17. A method of determining whether an agent affects a lymphoproliferative condition in a subject, comprising: a) administering said agent to a transgenic non-human animal whose genome comprises a nucleic acid construct comprising at least one transcriptional regulatory sequence capable of directing expression in B cells of the animal, operably linked to a nucleic acid encoding a miR155 gene product comprising a nucleotide sequence having at least 90% sequence identity to SEQ ID NO:1 and/or-SEQ ID NO:2; and b) after said agent has been administered to said transgenic animal, comparing one or more symptoms and/or indications of said lymphoproliferative condition in said transgenic animal to those of a control animal of the same genotype, wherein the control animal has not been administered said agent, wherein a difference in the detectability and/or rate of appearance of said one or more symptoms and/or indications of said lymphoproliferative condition in said transgenic animal, relative to said control animal, is indicative of the agent affecting the lymphoproliferative condition.

18. A method of testing the therapeutic efficacy of an agent in treating or preventing a lymphoproliferative condition in a subject comprising:

(a) administering said agent to a transgenic non-human animal whose genome comprises a nucleic acid construct comprising at least one transcriptional regulatory sequence capable of directing expression in B cells of the animal, wherein the transcriptional regulatory sequence is operably linked to a nucleic acid encoding a miR155 gene product comprising a nucleotide sequence having at least 90% sequence identity to SEQ ID NO:1 and/or SEQ ID NO:2; and

(b) after said agent has been administered to said transgenic animal, comparing one or more symptoms and/or indications of said lymphoproliferative condition in said transgenic animal with those of a control animal of the same genotype, wherein said agent has not been administered to said control animal; wherein if said agent inhibits, prevents and/or reduces said one or more symptoms and/or indications of said lymphoproliferative condition in said transgenic animal, relative to said control animal, then said agent is considered to have therapeutic efficacy in treating or preventing a lymphoproliferative condition in a subject .

19. The method as in any of the preceding claims, wherein the at least one transcriptional regulatory sequence comprises a VH promoter, an Ig heavy chain-Eμ enhancer or a combination thereof.

20. The method as in any of the preceding claims, wherein the transcriptional regulatory sequence is derived from mouse.

21. The method as in any of the preceding claims, wherein the nucleic acid comprises the nucleotide sequence of SEQ ID NO:1 and/or SEQ ID NO:2.

22. The method as in any of the preceding claims, wherein the transgenic animal is a mouse.

23. The method as in any of the preceding claims, wherein the lymphoproliferative condition is a B cell malignancy.

24. The method as in any of the preceding claims3, wherein the B cell malignancy is selected from the group consisting of acute lymphoblastic leukemia, B cell lymphoma, B cell neoplasm and a combination thereof.

25. The method as in any of the preceding claims3, wherein the B cell malignancy exhibits characteristics of human acute lymphoblastic leukemia, human lymphoblastic lymphoma or a combination thereof.

26. The method as in any of the preceding claims, wherein the lymphoproliferative condition is a preleukemia state.

27. The method as in any of the preceding claims, wherein the preleukemic state is characterized by pre-B cell proliferation.

28. The method as in any of the preceding claims, wherein the one or more symptoms and/or indications of said lyrnphoproliferative condition are selected from the group consisting of: an expanded population of B2201ow/CD191ow/CD101ow/ IgM-/TCR-/CD43- lymphoid cells, enlarged abdomen, splenomegaly, bone marrow replacement, lymphopenia and a combination thereof.